This invention relates to a grease composition for a high speed anti-friction or roller bearing and, more particularly, to a grease composition for a high speed roller bearing in which an urea thickener and specific additives are contained in a synthetic lubricant base oil.
Anti-friction bearings are employed in electrical components such as alternators used in motor cars, electro-magnetic clutches for car-laden air conditioners, idle pulleys or electrically actuated fan motors, or accessories such as fluid couplings for cooling fans, timing belt tensioners or air pumps. Mainly greases are employed for lubricating the rooler bearings.
Conventionally, as the grease for roller bearings, lithium soap greases employing relatively inexpensive mineral oils as the base oil, polyurea greases or greases, known as wide-range greases, in which the ester synthetic oils are thickened with lithium soap or sodium terephthalamate, are employed. If longer durability than that of the above greases or high temperature durability are required, greases employing silicone oil, fluorosilicone oil or fluorinated oil (perfluoro polyether oil) as the base oil are employed.
In automobiles, in keeping with the propagation of the FF cars aimed at reducing the size and weight of the vehicle, and with the demand for increasing the living space within the cars, the engine room space is necessarily reduced, while the electrical components and accessories with smaller size and weight are required. In addition, higher performance and higher output are demanded of the electrical components and the accessories, such that, in the case of an alternator, for example, it is necessary to increase its rotational speed by designing artifices to compensate for reduction in output caused by reduction in size. Moreover, in keeping with the demand for quiet operation, the degree of hermetic sealing of the engine room and the degree of heating within the engine room are elevated so that components capable of withstanding higher temperatures are necessitated. Presently, a longer service life of the bearings, less grease leakage, superior low temperature properties, superior rust-preventive properties and superior noiseless properties of the bearings are demanded of the greases for use with sealed bearings employed in electrical components and accessories of the motor cars.
Under these conditions, the conventional greases, such as mineral oil - lithium soap grease, mineral oil - polyurea grease or ester synthetic oil - lithium soap bearing under high temperature and high speed conditions, whereas the conventional greases such as the greases employing silicone oil, fluorosilicone oil or fluorinated oil as the base oil, are not fully satisfactory in that they fail to meet such properties as load withstanding properties, wear resistance, rust-preventive properties or noiseless properties, while being extremely expensive.
As a result of researches towards developing the long durability grease for use in high speed anti-friction bearings capable of satisfying the above mentioned properties required of the greases, the greases having synthetic oils as the base oils and urea compounds as the thickener have been found to exhibit various excellent properties as compared to the conventionally employed greases, and are presently attracting attention.
However, the high speed anti-friction bearings present a serious problem in that, since rust-preventive properties are required of the high speed anti-friction bearing, as mentioned hereinabove, rust-preventive agents need to be added to the grease and, should these agents be added in a required amount, the service life of the bearings, which is among the properties intrinsically required of the bearings, is lowered.